Middle voltage cable power lines relay protection against double ground faults influence to power supply reliability

Reliability of power system each element affects all power supply network reliability. The existing relay protection (RP) is not always able to effectively provide the cable lines thermal protection, especially in electrical cable networks, the neutrals of which are not directly earthed. To attain it, Universal relay protection against phase to phase faults was developed and patented in Latvian Republic (LV 13554 B). The invention has three objectives: 1) to modify and supplement existing RP so that it ensures not only cable line RP against phase-to-phase faults but also cable metal sheath RP against double ground faults; 2) to insure that RP, in case of double ground fault switches off only one of faulted lines, the second line with its customer remaining on duty; 3) to assign the switching off priority to one or several faulted lines in case of double ground fault.